1. Field of the Invention
This invention pertains generally to fluorescent lighting and, more particularly, to an electronic ballast system for fluorescent lamps.
2. Related Art
Heretofore, electronic ballasts have been provided for use with fluorescent lamps. Examples of such ballasts are found in U.S. Pat. Nos. 4,245,178 and 4,631,449.
Electronic ballasts typically operate at frequencies on the order of 10 KHz to 100 KHz, and are designed to provide high circuit efficiency, high reliability, and low cost. While the physical size and weight of ballasts are dependent upon operating frequency, with higher frequencies permitting ballasts to be smaller in size and lighter in weight, reductions in size and weight have not been easy to achieve.
In order to reduce losses, multiple wires or Litz wires have been used for transformer windings, but they add substantially to the cost of manufacture. The cost can be reduced somewhat by using single conductor, continuous windings on power transformers. However, that substantially reduces the coefficient of coupling and can result in high leakage flux which puts a heavy stress both on the transformer itself and on any switching devices or diodes used in the high energy path. In addition, leakage flux can also produce high voltage spikes and can cause electromagnetic interference in the nearby environment.
The higher flux drives and higher circulating currents required for reactive loading of a power transformer in prior systems can also increase core loss as well as loss in the windings themselves. To avoid such losses, it has heretofore been necessary to use larger cores and multiple conductors in the transformer windings.